Human skin pigmentation is important in determining susceptibility to skin cancer. It is a clinically obvious human trait, but very difficult to quantify accurately. Factors affecting skin color include hydration of the stratum corneum, blood flow, hemoglobin oxygenation and melanin. The amount of melanin, its pattern of distribution, the relative amount of the different melanins, pheomelanin and eumelanin all contribute to skin color.
Skin phototype is typically assessed subjectively by self assessment or a trained clinician using sun-exposed (SE) and sun-protected (SP) skin sites as well as hair and eye color, ethnicity, tan response and burn response according to Fitzpatrick Skin Type criteria (FST I-VI). Skin phototype is often used as a normalizing parameter in clinical studies as the basis for risk assessment for skin cancers; high risk=FST I, low risk=FST VI.
Phototype assessment has generally relied on self-assessment by the individual or clinician assessment using a variety of subjective parameters, including hair color, eye color, the number of freckles, tan response, burn response, and number of sunburns after 20 yrs of age. Both professional and self-assessment typically underestimate skin type, particularly those skin types most vulnerable to skin damage (e.g., photo damage), thus exposing the subject to a greater risk of disease (e.g. melanoma skin cancer) induced by improper protective care or by certain high risk activities (e.g., sun bathing). Determination of the type of melanin and quantification of melanin has typically required biopsy and HPLC analysis, which require expensive equipment and specialized training. In addition, these procedures are very time consuming.
Assessing phototype by subjective observation alone is problematic because of interoberserver variance. The disparity between the self-assessment vs. clinician-assessment of skin phototype poses further problems in phototyping.
Self- and Clinician-Assessed Skin Phototype Criteria:
SkinSkinSun burnPhotoTypeColorresponseSun tan responseIWhiteAlways & easilyNeverIIWhiteAlwaysMinimal & with difficultyIIIWhiteMinimalGradual & uniformly lightIVLight BrownMinimalAlways & Mod. brownVBrownRareProfuse & Dark brownVIBlackNeverMaximal & Black
There is a need for the study of skin type by non-invasive methods. For example, there is a need for an objective reflectance spectrophotometer method to determine skin phototype. Known techniques, such as known methods of reflectance measurements, are not sufficiently sensitive, accurate and/or reproducible enough for some purposes. More sensitive and objective techniques are needed, for example, to study the risk association between skin phototype and incidence of basal cell carcinoma, squamous cell carcinoma and melanoma. More sensitive objective techniques are also needed to quantify the changes in pigmentation over a long period of time and would be particularly useful in the study of pigmented nevi (i.e., moles), especially as they relate to the subsequent development of melanoma skin cancer.